1. Field of the Invention
The present invention relates to a structure of a semiconductor optical device, and a method for producing the semiconductor optical device.
2. Related Prior Art
A semiconductor optical device, in particular, the semiconductor layer diode generally provides a buried mesa structure to reduce the threshold current. However, when the doping concentration in layers coming in contact with the side walls of the mesa is high, the impurities contained in the layers neighbor to the mesa may diffuse into the active layer in the mesa, which degrades the quality of the device, especially, the light emitting efficiency of the laser diode. Japanese Patent Applications published as H11-238942A and H07-254750A have disclosed semiconductor light-emitting devices with a structure where the inner layer and the outer layer in the buried region have different doping concentration of zinc (Zn) to suppress the Zn diffusion into the active layer.
However, because of the large diffusion co-efficient of Zn, it is quite difficult to prevent the invasion of Zn on the active layer completely. The present invention is to provide a new structure of the semiconductor optical device to prevent the Zn diffusion into the active layer effectively and a method to produce the device.